In general, brake apparatuses of vehicles are configured to generate the pressure of brake fluid in the master cylinder in response to brake pedal operation and distribute the fluid pressure to wheel cylinders through a plurality of pipelines. Any air in the pipelines would cause a time delay between the start of brake application and the actual start of braking, which in turn causes problems; for example, the driver may feel that something is wrong in the brake pedal operation.
To solve such problems, conventional brake apparatuses are configured to detect the presence of any air in the pipelines by computing response speed of a change in fluid pressure when transmitting fluid pressure from the master cylinder to the brake pipelines (see Patent Document 1 listed below).